Injection molding machine

Abstract

If a screw is moved forward after a metering step is completed, the screw moves in a state where a check ring on a tip end of the screw is in open state. Resin flows in a direction opposite to the injection direction. A rotational force is applied to the screw due to the backflow of the resin. If the check ring closes a resin passage, the rotational force acting on the screw is reduced. A peak time of the screw rotational force is detected as closing point in time of the check ring. Physical amounts such as a screw rotational force and a screw position at that timing are detected. Since the closing point in time of the check ring is precisely detected, correction of the injection / hold pressure switching position and the injection speed switching position can be adjusted more precisely. It is possible to precisely determine whether a molded article is non-defective or defective based on the detected physical amount.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an injection molding machine having a screw provided with a check ring.[0003]2. Description of the Related Art[0004]There is conventionally used an injection molding machine having an injection mechanism whose screw provided at its tip end with a check ring mechanism so as to prevent backflow of resin at the time of injection like an in-line screw type injection molding machine. FIG. 1 shows one example of the check ring mechanism. The screw 1 is provided at its tip end with a screw head 2. A portion of the screw 1 which is reduced in diameter is provided between the screw head 2 and a main body of the screw 1. A check ring 3 is provided at the diameter-reduced portion such that the check ring 3 can move in an axial direction of the screw. A check seat 4 is provided at the diameter-reduced portion and on the side of the main body of the screw 1. The check seat 4 comes into intimate conta...

AI Technical Summary

Benefits of technology

[0021]Hence, it is an object of the present invention to make it possible to more precisely detect closing point in time of check ring without using a special mechanism. It is another object of the invention to make it possible to determine whether a molded article is non-defective or defective, and to adjust a molding condition based on detected closing point in time.

[0032]According to the present invention, since the closing point in time of the check ring can be detected more precisely, it is possible to easily and more precisely adjust the molding conditions such as the injection / hold pressure switching position and the switching position of the injection speed by the detected various physical amounts at the closing point in time of the check ring. Further, it is possible to more precisely determine whether a molded article is non-defective or defective based on the various physical amounts at the closing point in time of the check ring.

Problems solved by technology

If the check ring 3 retracts and timing for closing the resin passage is varied, an amount of resin to be charged is also varied and the molding becomes unstable.

However, there is a problem that a pressure remains a groove 6 between flights 5 and the screw 1 behind the check ring mechanism immediately before injection, and the closing point in time is varied due to the remaining pressure.

Therefore, the injection capacity is varied between cycles due to the variation of the closing point in time and as a result, this affects quality of a molded article.

In this case, if a pressure sensor which comes into direct contact with resin is mounted, it is inevitable that a fine step is generated on inner surface of a cylinder, such an adverse influence that a carbide caused by remaining resin is mixed into a molded article can not be avoided.

Further, since a distortion of a cylinder is indirectly detected without direct contact with resin, the detection precision is deteriorated in the case of a pressure sensor which detects a resin pressure.

There are problems that any type of pressure sensor is expensive and its handling is troublesome, periodical maintenance and calibration are required.

According to the technique for detecting the closing point in time of the ring valve by detecting the capacitance as described in the above patent document, there are drawbacks that the conductive member for detecting the capacitance must be disposed in the screw, a hole through which a wire passes must be formed in a center of the screw, a slip ring for taking out a measurement signal must be disposed in the screw and means for measuring the capacitance must be added, and the structure becomes complicated.

Therefore, a resin pressure in front of the screw head is also applied to the sensor, and it is difficult to detect a force Fx in the axial direction component of the force flown-back resin acts on the flight.

Therefore, in the case of the method for detecting the close of the check ring from the rotation amount of the screw as in the technique described in the above patent document, there is a possibility that the detection of the closing point in time includes an error.

The technique described in the above patent document has a problem that the special backflow preventing mechanism which interrupts the metering portion and the screw head by reversely rotating the screw after the metering is completed is required, and this technique can not be applied to a molding machine having a general backflow preventing mechanism.

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